1. Field of the Invention
The present invention relates to a vehicular radar apparatus comprising a malfunction detecting device and a method for detecting a malfunction of the radar apparatus.
2. Description of Related Art
Vehicular radar apparatuses for detecting relatively approximate and immobile obstacles, such as trolley poles and concrete fences, in order to prevent vehicles (for example, automobiles) from colliding with the obstacles for example while parking the vehicle in a garage, have been conventionally implemented. Furthermore, in recent years, in addition to the radar apparatus for the detection of immobile obstacles as described above, research and development have been carried out for implementing a radar apparatus for the acquisition of moving objects over relatively long distances at high accuracy and at high speed. Such a radar apparatus can be used, for example, as an alarm system for preventing colliding with or rear-ending another car while driving, or an adaptive cruse control (ACC) used for auto cruising.
U.S. Pat. No. RE 36,095 which belongs to the assignee of the present application discloses a multi-beam radar apparatus which uses a high frequency beam in the millimeter waveband as a radar wave. This multi-beam radar apparatus comprises a plurality of transmitter receivers for radiating and receiving radar beams so that the radar beams spatially overlap with each other, and it is possible to improve the accuracy of detection by optimizing the combination of the transmitter and receivers.
European Patent Application No. EP0840140A1 filed by the assignee of the present application discloses a scanning beam radar apparatus which uses a high frequency beam in the millimeter waveband as a radar wave. In this scanning beam radar apparatus, a primary transmitter radiates a high frequency beam, and the beam is scanned by a rotating reflector. The scanned beam is converged by a dielectric lens in order to decrease the scanning angle of the beam, and is radiated toward the running direction of the vehicle.
However, in the above multi-beam radar apparatus, each of the transmitter receivers has an inherent detection area, and the position of a detected object, that is, the direction with respect to a vehicle and the distance between the object and the vehicle, is calculated by collating a plurality of data from the selected transmitter receivers. Therefore, when a malfunction or a sensitivity degradation due to deterioration occur in any one of the selected transmitter receivers, it becomes necessary to detect which receiver has a malfunction or a sensitivity degradation.
In contrast, in the case where the above scanning beam radar apparatus uses only one transmitter receiver, when a sensitivity degradation occurs in the transmitter receiver, it becomes necessary to compensate the sensitivity in all directions.
Also, in the above conventional radar apparatuses, in order to check the radar sensitivity, it is necessary to transport a vehicle comprising a radar apparatus to a predetermined position in a testing station where a reference object is provided and to activate the radar apparatus to measure its receiving sensitivity with respect to the reference object. Therefore, a periodic check of the conventional apparatus requires a laborious process and a high costs. Furthermore, in the conventional radar apparatuses, it is difficult to check the radar sensitivity at an arbitrary time other than the periodic checks.
Additionally, because the conventional radar apparatus is generally installed at the front or rear end of a vehicle, such as in a bumper or in a front grille, it is susceptible to the adverse effects of rain, snow, wind, dust, and mud. In particular, the radar sensitivity decreases when snow or mud is thickly attached to the radar apparatus. Accordingly, some countermeasure for preventing such effects is necessary. Furthermore, in the case of installing the radar apparatus in the vicinity of the engine compartment, it is necessary to improve the heat resistance of the radar apparatus, which increases the manufacturing costs of the radar apparatus.